This invention relates to an image processing apparatus, particularly one that is useful in reading the images on photographic films (which are hereinafter referred to simply as xe2x80x9cfilmsxe2x80x9d) to produce photographic prints in succession, more particularly one that is useful in reproducing a gray in a stable manner to produce photographic prints of high quality in succession.
Heretofore, the images recorded on films such as negatives and reversals have been commonly printed on light-sensitive materials (photographic paper) by means of direct (analog) exposure in which the film image is projected onto the light-sensitive material to achieve its areal exposure.
A new technology has recently been introduced and this is a printer that relies upon digital exposure. Briefly, the image recorded on a film is read photoelectrically, converted to digital signals and subjected to various image processing operations to produce image data for recording purposes; recording light that has been modulated in accordance with the image data is used to scan and expose a light-sensitive material to record a latent image, which is subsequently developed to produce a finished print. The printer operating on this principle has been commercialized as a digital printer.
In the digital printer, images can be processed as digital image data to determine the exposure conditions for printing. Hence, it is capable of performing various image processing operations such as the correction of washed-out highlights or flat (dull) shadows due to the taking of pictures with backlight or an electronic flash, sharpening and the correction of color or density failures and this enables the production of prints of the high quality that has been impossible to achieve by the conventional direct exposure. Further, not only the assembling of images and the splitting of a single image into plural images but also the composition of characters can be performed by processing the image data and, as a result, prints can be outputted after various editing and/or processing operations have been performed in accordance with specific uses.
Outputting images as prints is not the sole capability of the digital printer; the image data can be supplied into a computer and the like and stored in recording media such as a floppy disk; hence, the image data can be put to various non-photographic uses.
Having these features, the digital printer is basically composed of an image input unit having a scanner (image reading apparatus) and an image processing apparatus, and an image output unit having a printer (image recording apparatus) and a processor (developer).
In the scanner, reading light issuing from a light source is allowed to be incident on a film, from which projected light bearing the image recorded on the film is produced and focused by an imaging lens to form a sharp image on an image sensor such as a CCD sensor; the image is then captured by photoelectric conversion and sent to the image processing apparatus as data for the image on the film (as image data signals) after being optionally subjected to various image processing schemes.
In the image processing apparatus, image processing conditions are set on the basis of the image data captured with the scanner and image processing as determined by the thus set conditions is performed on the captured image data and the resulting output image data for image recording (i.e., exposure conditions) are sent to the printer.
In the printer, if it is of a type that relies upon exposure by scanning with an optical beam, the optical beam is modulated in accordance with the image data from the image processing apparatus and deflected in a main scanning direction as the light-sensitive material is transported in an auxiliary scanning direction perpendicular to the main scanning direction, whereby a latent image is formed as the result of exposure (printing) of the light-sensitive material with the image bearing optical beam. Then, in the processor, development and other processings as determined by the light-sensitive material are performed to produce a print reproducing the image that was recorded on the film.
The image processing schemes described above generally include color balance adjustment, contrast correction (toning), lightness correction, dodging (compression/extension of the dynamic range of densities), chroma correction and sharpening. These schemes are performed by known methods comprising appropriate combinations of arithmetic operations with operation expressions, processing operations with retrieving tables, namely, look-up tables (LUTs), matrix (MTX) operations, processing operations with filters and the like. For example, color balance adjustment, lightness correction and contrast correction are performed with LUTs, while chroma correction is performed by MTX operations. Sharpening and dodging are performed in other processing units.
In three dimensional retrieving tables, namely, 3D (3 dimensional)-LUTs which have been used in the conventional image processing technology, output signal values are held corresponding to respective vertexes of a cube constructed with planes perpendicular to R, G and B axes and then output signal values, namely, nonlinear transformation values by LUTs, at a position are obtained by subjecting the thus held output signal values corresponding to respective vertexes to interpolation operations by means of weights in accordance with the position within the cube. However, a problem with such processing is that input signal values of xe2x80x9cgrayxe2x80x9d may cause a subtle variations different from its aim in an output signal, unless sufficient number of planes perpendicular to R, G and B axes are prepared.
In order to solve the problem, the number of planes perpendicular to R, G and B axes may be increased for preparing exquisite cubes. However, another problem will come out in this case such that output signal values corresponding to respective vertexes of huge values of cubes must be held.
The present invention (hereinafter called as the invention) has been accomplished under these circumstances and has as an object providing an image processing apparatus that realizes a three-dimensional retrieving table (3D-LUT) which does not cause subtle variations different from its aim in output signals only with a small addition of memory, capacity to the ordinary memory thereby ensuring that the gray reproduction can be performed consistently and that photographic prints of high quality are produced in succession.
The stated object of the invention can be attained by an image processing apparatus having nonlinear processing means for performing nonlinear processing on digital color signals, the nonlinear processing means comprising: gray region discriminating means for discriminating whether the digital color signals are present in a gray proximate region including gray signals; and region correspondence nonlinear processing means for performing the nonlinear processing differently in accordance with cases where the digital color signals are discriminated as signals inside the gray proximate region being present in the proximity of the gray signals or as signals outside the gray proximate region being not present in the proximity of the gray signals by the gray region discriminating means.
It is preferable that, in the image processing apparatus, the region correspondence nonlinear processing means comprises first processing means for calculating endpoints of a first interpolation unit region including the signals inside the gray proximate region as well as first interpolation weights of the signals inside the gray proximate region; second processing means for calculating endpoints of a second interpolation unit region including the signals outside the gray proximate region as well as second interpolation weights of the signals outside the gray proximate region; and interpolation processing means for performing interpolation processing using the endpoints of the first interpolation unit region and the first interpolation weights which have been calculated by the first processing means to obtain nonlinear processing output values of the signals inside the gray proximate region or for performing another interpolation processing using the endpoints of the second interpolation unit region and the second interpolation weights which have been calculated by the second interpolation processing means to obtain nonlinear processing output values of the signals outside the gray proximate region.
It is also preferable that the first processing means comprises: first address calculating means for calculating first address output values of the signals inside the gray proximate region as data of the endpoints of the first interpolation unit region; first interpolation weight calculating means for calculating the first interpolation weights using the signals inside the gray proximate region; and first storing means for storing the first address output values obtained by the first address calculating means, and wherein the second processing means comprises: second address calculating means for calculating second address output values of the signals outside the gray proximate region as data of the endpoints of the second interpolation unit region; second interpolation weight calculating means for calculating the second interpolation weights using the signals outside the gray proximate region; and second storing means for storing the second address output values obtained by the second address calculating means.
It is further preferable that the interpolation processing means performs the interpolation processing using the first address output values stored in the first storing means and the first interpolation weights calculated by the first interpolation weight calculating means when the digital color signals are discriminated as being present in the gray proximate region or perform the interpolation processing using the second address output values stored in the second storing means and the second interpolation weights calculated by the second interpolation weight calculating means when the digital color signals are discriminated as being not present in the gray proximate region, thereby obtaining the nonlinear processing output values.
It is also further preferable that the nonlinear processing means is three dimensional retrieving table transforming means for performing the nonlinear processing using a three dimensional retrieving table.
It is still further preferable that the digital color signals comprise three primary color signals of red(R), green(G) and blue(B), wherein the interpolation processing means holds output signal values corresponding to each vertex of an cube composed of planes perpendicular to red(R), green(G) and blue(B) axes as data of the endpoints of the interpolation unit region in the three dimensional retrieving table, performs an interpolation operation of the output signal values corresponding to each vertex with interpolation weights corresponding to a position within the cube and wherein the cube in proximity of the gray signals, which is present inside the gray proximate region is rendered smaller in size than the cube in a periphery of the three dimensional retrieving table, which is present outside the gray proximate region. Moreover, it is preferable that a side of the cube in the proximity of the gray signals is half or less in the size of the side of the cube in the periphery. Furthermore, it is preferable that the gray proximate region in the proximity of the gray signals is a region where total length from the gray signals as a center in each direction of the red, the green and the blue axes is within 5 pieces of cubes in the periphery. Still furthermore, it is also preferable that the nonlinear processing means performs at least one nonlinear processing of color balance adjustment, lightness correction and contrast correction.